QUESTIONS TO ASK WHEN DETERMINING WHETHER OR NOT IT’S WORTH IT TO HARVEST YOUR RESIDUE
there is lots of talk these days about crop residue removal for bioenergy purposes. Although the agricultural industry works hard to make it clear to those less familiar with farming that crop residue has real value, there is still some confusion. The value hinges on a few components:
- Crop residue is critical in maintaining the organic matter fraction of the soil, which in turn impacts everything from yield potential to water holding capacity and resistance to compaction.
- When left on the surface or incorporated in shallow surface soil layers, crop residue is critical to soil erosion prevention.
- Crop residue has value based simply on the nutrients that would be lost if these residues were removed from the field.
- Value is attributed to residue based on the current price being paid for traditional uses such as straw for bedding and mushroom compost.
TABLE 1. NUTRIENT REMOVAL AND VALUES FROM 1 TONNE OF DRY CORN STOVER.
|Price of Fertilizer ($/tonne)||$500.00
|Value of Nutrient in Stover ($/tonne)||$8.51||$2.98||$11.24||$22.73|
|Price of Fertilizer ($/tonne)||$750.00
|Value of Nutrient in Stover ($/tonne)||$12.77||$4.46||$16.86||$34.09|
what’s it worth?
So what is crop residue worth? Well the simple answer would be to pick up the phone and find out what someone would pay you for the wheat straw or corn stalks on your land.
However, slightly more complicated, but certainly not impossible, is determining the value of the nutrients in the residue. Table 1 gives the estimates for nutrient concentrations in a tonne of corn stover, some fertilizer costs and the resultant fertilizer replacement value. At relatively modest fertilizer prices, the nitrogen-phosphorous-potassium (NPK) removal is valued at $22.73 per tonne of stover. The P and K values are pretty straight forward. But, the N cost is more complicated – that is, should I really value the N in the stover when in fact if I remove the corn stalks I may indeed lower my nitrogen costs the next year if I were to grow corn again? This will lead us to the more complex issues which demand that we consider the value of the organic matter not just the nutrients; that we consider long-term impacts not just next year’s budgets.
If you would like to evaluate the nutrient value in various crop residue scenarios Ken Janovicek from the University of Guelph and I have put together a calculator for this purpose. The calculator allows you to look at different levels of crop yield, costs associated with residue collection and prices for fertilizer, among other factors. It also presents some assumptions that you may or may not agree with. It is hosted on the Innovative Farmers Association of Ontario website at www.ifao.com.
The next step in determining the value of crop residue is looking at the value of the residue as it relates to long term soil health, organic matter levels and sustainable productivity. The first question to ask is: How much crop residue does it take to fuel the organic matter furnace that exists in your soil? Organic matter is constantly being broken down by a variety of processes; in order for soil organic matter levels to remain steady in an agricultural soil, crop residues need to feed this cycle. The estimates for this are fairly wide ranging depending on soil factors. But, a reasonable estimate is 10,000 kilograms per hectare per year (kg/ha/year); that is 10 tonnes of crop residue (including roots) to keep soil organic matter levels from declining.
TABLE 2. TOTAL CROP RESIDUE PRODUCTION (ABOVE AND BELOW GROUND COMPONENTS) FROM A THREE CROP ROTATION, ESTIMATES PROVIDED BY HILLA KLUDZE ET. AL., UNIVERSITY OF GUELPH, 2010. HTTP://IFAO.COM/IFAO-SOILSUSTAINABILITY.HTML (SEE CROP RESIDUE VALUE ESTIMATOR)
|Grain Yield (bu/ac)||162||44||80|
|Total Residue (kg/ha)||17,147||5,658||11,919|
On average, the crop residue produced in the corn-soy-wheat rotation shown in Table 2 is 11,575 kg/ha/year. This data is from an ongoing project at the University of Guelph to evaluate crop residue availability.
The key message here is that if it takes 10,000 kg/ha/year to simply maintain soil organic matter levels, the amount of crop residue you could remove without some impact on productivity would be quite small. Higher crop yields, manure additions, cover crops and tillage would all play a part in assessing the value of crop residue. However, it is clear that underestimating the amount of crop residue required for stable organic matter levels, may contribute to undervaluing the crop residues. •